The present disclosure relates to burner assemblies, and particularly to oxygen-fuel burner assemblies. More particularly, the present disclosure relates to pulverized solid fuel combustion systems.
Many types of coal and other solid fuels can be burned successfully in pulverized form. Coal is pulverized and delivered to fuel-burning equipment and then combusted in a furnace to produce heat for various industrial purposes.
A burner is used to “fire” pulverized coal and other solid fuels. In a direct-firing system, the coal is delivered to the burner in suspension in a stream of primary air, and this mixture must be mixed with a stream of secondary air at the burner.
One challenge facing the burner industry is to design an improved burner that produces lower nitrogen oxide emissions during operation than conventional burners. Typically, an industrial burner discharges a mixture of fuel and either air or oxygen. A proper ratio of fuel and air is established to produce a combustible fuel and air mixture. Once ignited, this combustible mixture burns to produce a flame that can be used to heat various products in a wide variety of industrial applications. Combustion of fuels such as natural gas, oil, liquid propane gas, low BTU gases, and pulverized coals often produce several unwanted emissions such as nitrogen oxides (NOx), carbon monoxide (CO), and unburned hydrocarbons (UHC).
According to the present disclosure, a burner assembly is provided for combining oxygen and fluidized, pulverized, solid fuel to produce a flame. The burner assembly includes an oxygen supply tube adapted to receive a stream of oxygen and a fuel supply tube arranged to extend through the oxygen supply tube to convey a stream of fluidized, pulverized, solid fuel into a flame chamber. Oxygen flowing through the oxygen supply tube passes through oxygen-injection holes formed in the fuel supply tube and then mixes with fluidized, pulverized, solid fuel passing through the fuel supply tube. Thus, an oxygen-fuel mixture is created in a downstream portion of the fuel supply tube and discharged into the flame chamber. This mixture is ignited in the flame chamber to produce a flame.
In illustrative embodiments of the disclosure, the fuel supply tube extends into and through the oxygen supply tube to define an annular oxygen flow passage extending around and along an annular exterior surface of the fuel supply tube in a direction toward the flame chamber. Oxygen flows through this annular oxygen flow passage to reach outer oxygen-inlet openings in the oxygen-injection holes formed in the annular exterior surface of the fuel supply tube.
In one embodiment, the fuel supply tube includes a solid-fuel conduit and an oxygen-fuel nozzle coupled to the solid-fuel conduit and formed to include the oxygen-injection holes. Oxygen and fluidized, pulverized, solid fuel are mixed in the nozzle to create a combustible mixture that is then discharged into the flame chamber and ignited to produce a flame.
In illustrative embodiments of the disclosure, means is provided for mixing some of the oxygen extant in the oxygen flow passage provided in the oxygen supply tube with the oxygen-fuel mixture that is discharged from the fuel supply tube into the flame chamber. In this case, a first portion of the oxygen flowing through the oxygen flow passage is mixed with the stream of fluidized, pulverized, solid fuel just before that fuel exits the fuel supply tube and a remaining portion of the oxygen flowing through the oxygen flow passage is mixed with the oxygenated steam of fluidized, pulverized, solid fuel in a region located outside the fuel supply tube and near an oxygen-fuel outlet opening formed in the fuel supply tube to provide supplemental oxygen to that oxygenated fuel stream.
Additional features of the present disclosure will become apparent to those skilled in the art upon consideration of the following detailed description of illustrative embodiments exemplifying the best mode of carrying out the disclosure as presently perceived.